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Thursday, 6-May-2010 10:42 Email | Share | | Bookmark
A Definition Of Programmable Logic Control

Programmable Logic Control or PLC is frequently named the work horse in manufacturing mechanization. We aren't able to assume how the production run lacking it as it is truly important due to all production process go through a unchanging repetitive sequence of operations that include logical ladder and decisions. Hence, what is a PLC for? It is used to manage, time and regulate the series. The PLC is considered necessary to control sequence of procedures in automatic manufacturing system.

Fundamentally, PLC was hard wired with electronic relays, timers and logical units. The logical control system had to be by hand changed or rewired if the machining list was also changed. It was not elastic, of course, and the firmness sometimes spent more time while the company has to re-arrange the production timetable. That condition was before 1970 while the computers were not on handIexist.

When little computers were created, switching, time delays and logic are not a considerable obstacle once more as the engineers have finished computer programs that are easy to be adjusted when the control obstacle changes. Also, the computer programs construct new logical functions than hardwired logic control.

These days once microprocessors have various enhanced features and lots of functions, a cheap PLC is able to even run a medium scale automatic machining station while a huge Programmable Logic Control is able to manage all automation systems.

The PLC consists of 4 central units as follows:
1. A programme memory - to store all instruction of the logical control sequence
2. The Data Memory - to store the status of switches, interlocks, past values of data and other working data
3. The output device -- including hardware and software drivers for manufacturing process actuators, such as solenoid switches, motors and valves
4. The input Devices - consisting hardware and software drivers for industrial process sensors such as status sensors, proximity detectors, interlock settings and so on.

In addition, Programmable Logic Control has programming units that is applied to construct, check and edit the logical sequence that PLC will implement. They are commonly a simple form of assembly code. Each company has their own standard and definition of these codes. There are other programming languages, consisting the IEC 61131-3 standard, sequential Function chart and Function Block Diagrams. On the other hand, a long established standard programming language for programmable logic, called "ladder Logic" is regularly named by PLC programmers.

In recent times, the plc programming has amazingly developed. Hence, it is sometimes complicated to put all features into ladder logic framework and the different programming languages are becoming more generally used. At this time nevertheless, ladder logic is the regular way to explain a Programmable Logic Control programme.


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